This section provides background information related to the present disclosure which is not necessarily prior art.
Internal-combustion engines for vehicles are provided with electronic fuel injection systems having one or more fuel injectors for admitting fuel to the combustion chamber of the engine. For reasons of fuel efficiency and exhaust emissions reduction, it is of importance to be able to control precisely the volume of fuel injected by one or more fuel injectors into each cylinder of the engine. In practice, fuel injection systems have at least one injector for each cylinder of the engine and an electronic control unit for controlling each injector individually. Flow-rate variance from injector to injector may occur due to manufacturing variances and/or as a result of injector ageing. In this regard, flow-rate means the amount of fuel passing through the injector per unit of time at a given fuel pressure. The electronic control unit is able to produce control signals that control energization or open time of each injector. The amount of fuel injected, however, can vary in the flow-rate characteristics which may be encountered amongst injectors fitted in the same injection system and over the lifetime of the engine.
In order to compensate for such flow rate variance, calibration cycles are implemented by which measurements are taken relating fuel injection flow rate and injector energization time in order to provide fuel injection gain data. The fuel injection gain data is provided in a map in memory for use in generating control signal for operating the engine. The map relates target fuel injection volume, energization time, rail pressure and injector ID. The map is initially established at manufacturing and may be adjusted throughout the lifetime of the engine. In order to determine the adjusted maps during the operative lifetime of the engine, measurement cycles are run during an engine idle condition at various lower rail pressures, but measurement cycles are not run for higher rail pressure. Such a system may compromise the accuracy of the fuel injection gain data for the higher rail pressures. However, performing the measurement cycles at the higher rail pressure may not be acceptable because of perceptible engine noise in the idle state.
It should also be appreciated that there is a trend to operate engines more in higher rail pressure conditions for efficiency and fuel emission reasons.
Accordingly, it is desirable to establish fuel injection gain data for use in controlling fuel injectors in a time efficient, and accurate way that is operable at high rail pressures without unacceptable engine noise. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.